Rare-earth material lights up with a message when stretched

A material that lights up when stretched or placed under UV light could make bank notes harder to counterfeit.

Mechanoluminescent materials light up when they’re rubbed, bent, or stretched. Songshen Zeng at the University of Connecticut and his colleagues have made a new one using rare earth elements.

When a rubbery strip of it is stretched, charged particles within its molecular structure gain energy and are jostled out of their places. As they settle back in, they release that extra energy in the form of light.